The hemagglutinin protein of influenza virus has a globular head domain which is highly heterogeneous among flu strains and a stalk region containing a fusion site which is needed for entry into the cells. The hemagglutinin protein (HA0) is activated to permit the fusion site to effect virulence by cleavage into HA1 and HA2 portions which remain coupled using disulfide bonds but undergo a conformational change. This cleavage site contains a consensus sequence which is shared both by influenza A and influenza B and by the various strains of influenza A and B.
Bianchi, E., et al., J. Virol. (2005) 79:7380-7388 describe a “universal” influenza B vaccine based on the consensus sequence of this cleavage site which was able to raise antibodies in mice when conjugated to the outer membrane protein complex of Neisseria meningitidis. Monoclonal antibodies which appear to bind to the consensus sequence were also described. In addition, successful passive transfer of antiserum was observed in mice. Prior vaccines, such as those described in WO2004/080403 comprising peptides derived from the M2 and/or HA proteins of influenza are subject to inducing antibodies that are either of weak efficacy or are not effective across strains.